Fresh water from rivers or lakes is treated in a water plant to convert the raw water into water for human consumption meeting accepted purity standards. The processes used have been honed over the years to produce high quality potable water from raw water at surprisingly low costs.
The primary treatment in a water plant occurs in a clarifier where a flocculant is added to raw water. A water plant clarifier is a large sized, round or rectangular concrete structure. The flocculent causes particles suspended in the water to coagulate, subsequently growing in size and weight. The clarifier is sized to provide sufficient residence time for the majority of the solids to drop out of suspension. Water is then passed through sand filters, perhaps treated with activated carbon, chlorinated and possibly fluoridated before being delivered to water supply mains which transport the treated water to residences, businesses and industries.
One of the recurrent problems in water treatment plant operations is the growth of algae in the clarifier and sand filters. Algae come in many types including filamentous algae, such as Cladaphora and Spirogyra, planktonic algae such as Microcystis and Anabaena, branched algae such as Chara vulgaris and Nitellam, swimming pool algae commonly referred to as black, brown and red algae and algae found in ponds such as Dictyosphaerium, Spirogyra, Oedogonium, Chlorococcum, Pithophora, Hyudrodictyon and Lyngbya. It is not uncommon to see a municipal water plant clarifier with a beard of algae around its peripheral walls and filamentous algae growths several feet long.
As used herein, the term municipal water plant is intended to mean a water plant used in treating raw water and converting it to potable water for human consumption, regardless of whether the entity doing so is public or private.
Algae blooms have been noted to appear literally overnight under the right temperature and sunlight conditions and, if left untreated, will cause taste and odor problems in the finished waters. The problems caused by algae in municipal water plants are handled in a variety of ways by current treatment methods. The odor and taste problems which typically recur during periods of high summer temperatures and long daylight hours occur from detritus thrown off by algae in the clarifier. Not all of this detritus is removed by sand filters. Any detritus passing through the sand filters is converted in the final chlorination process to a family of chloro-organic compounds which cause the objectionable smell and taste that consumers complain about.
The standard treatment for controlling algae in municipal water plants is to scatter crystals of cupric sulfate pentahydrate, CUSO.sub.4.5H.sub.2 O, which is also known by its common name blue vitriol, into the clarifier. Blue vitriol is commercially available in 50 pound bags having crystals ranging in size from fine (1/8") to large (1"). Scattering is done with a shovel, a scoop, or by hand. Ideally, the crystals dissolve in the water so the copper ion is present in the water. The soluble or active copper (II) ion kills algae because of its effect on chlorophyll which is a large porphyrin structure occurring either as blue-green chlorophyll-a or yellow-green chlorophyll-b. Both molecules have four centrally placed nitrogen atoms which complex a single magnesium atom. The magnesium removes carbon dioxide from the water and delivers it to the algae thus allowing photosynthetic growth. The soluble copper (II) ion replaces the magnesium by forming a stronger porphyrin complex, which does not bond with carbon dioxide. The algae dies by virtue of its growth mechanism being squelched by a lack of carbon dioxide, in a process analogous to the chemical poisoning of hemoglobin in mammals. A small part of the algicidal copper exits the treated water stream in the clarifier sludge and not with the finished water because it has been intimately bonded to the algae chlorophyll. A large part of the copper sulphate is believed to remain undissolved and drops into the clarifier sludge as copper hydroxide coated pellets. One of the inherent advantages of copper algicides is that algae cannot mutate or evolve to avoid its effect. No amount of evolution can prevent copper from displacing magnesium in the chlorophyll and no amount of evolution can cause the copper porphyrin to absorb carbon dioxide.
Disclosures of some interest are found in U.S. Pat. Nos. 3,844,760; 4,012,221; 4,505,734 and 5,541,150.